Defective pixels are pixels on a liquid crystal display (LCD) that are not performing as expected. Defective pixels in LCDs generally fail to reproduce light levels correctly. There are several variations of defective pixels in LCD's, including dark dot defects, bright dot defects, partial sub-pixel defects, tape automated bonding (TAB) faults, and stuck sub-pixels.
In LCD manufacturing, it is common for a display to be manufactured that has a number of sub-pixel defects, wherein each pixel is composed of three primary-colored sub-pixels (i.e. RGB or CMYK color models). The number of faulty pixels tolerated, before a display is rejected, is dependent on the class that the manufacturer has given the display (although officially described by the ISO 13406-2 standard, not all manufacturers interpret this standard the same way, or follow it at all). Some manufacturers have a zero-tolerance policy with regard to LCD displays, rejecting all units found to have any number of (sub-)pixel defects. Displays meeting this standard are deemed Class I. Other manufacturers reject displays according to the number of total defects, the number of defects in a given group (e.g., 1 dead pixel or 3 stuck sub-pixels in a 5×5 pixel area), or other criteria.
Furthermore, many mobiles devices have touchscreens that are vulnerable to imperfections, including scratches. While touchscreens have become harder, mobile devices still are susceptible to imperfection from even harder materials.
Generally, mobile devices, including tablets and phones, use LCD displays and touchscreens to cover the LCD displays. With the increasing usage of computer network services all over the world, these mobile devices are in great demand. As a result, the cost of used mobile devices has increased. However, as with any used devices, the used mobile device needs to be tested to determine operability, especially with respect to the working displays and imperfections. There is a need to efficiently and effectively detect defective pixels and screen imperfections of new and used mobile devices.